This invention relates to electronic displays and, more specifically, to a method and apparatus for driving an external electrode discharge display panel or plasma display panel in a time division fashion.
External electrode discharge display panels and circuits for driving such displays are described in a prior U.S. patent application Ser. No. 388,787 filed Aug. 16, 1973 now U.S. Pat. No. 3,869,644, by Akira Yano et al. German patent application No. P 23 42 359.5 filed Aug. 21st, 1973).
As described in the prior patent application, one of the conventional driving circuits comprises means for cyclically supplying a driving pulse train of a predetermined duration to the electrodes of a first electrode group, such as the row electrodes array, of a plasma display panel, and means for selectively supplying another driving pulse train of the opposite phase or polarity to the electrodes of a second group, such as the column electrodes. An intermittent gas discharge occurs in a gas discharge cell of the plasma display panel interposed between the spatially opposing electrodes simultaneously supplied with the drive pulse trains. If the frequency of the intermittent gas discharge is sufficiently high (for example, 10 kHz), the selected cells glow forms an observable display of a numeral, a letter, a symbol, and/or a combination of these.
In one of the conventional driving circuits, use is made of drivers comprising transistors connected to the electrodes through collector resistors. When the electrodes are not selected, the associated transistors are rendered nonconductive and the electrodes are either connected to a source of a d.c. voltage V.sub.O or to ground through the corresponding collector resistors. When a certain row electrode C.sub.k is not selected while the adjacent several row electrodes are selected, the row electrode C.sub.k is supplied with a spurious voltage pulse derived by differentiation of the pulse voltages supplied to the adjacent row electrodes with a time constant RC, where R represents the resistance of the collector resistor connected to each of the row electrodes and C represents the total electrostatic capacitance comprising the electrostatic capacities between the row electrode C.sub.k and the adjacent row electrodes, and the stray capacitance between the wiring to the row electrode C.sub.k and conductors for the adjacent row electrodes. Although the driving circuit of this type is preferable because of the simplicity of its circuitry, the spurious voltage pulse often results in an undesired display.
In order to attain stable operation of the driving circuit, it is necessary to restrict the potential V.sub.O supplied by the d.c. source. That is, the driving circuit has been operable only in a limited range of the driving pulse voltage. The time constant RC may be reduced by a reduction in at least one of the resistance R and the total electrostatic capacity C. Reduction of the capacitance C may readily be achieved by enlarging the display panel. However, this is contrary to the general requirement for a compact display panel. Reduction of resistance R results in an increase in the power consumption when the transistors are turned on to provide a desired display.
Besides the driving circuit of the type described above in some detail, a driving circuit comprising drivers exhibiting a high output impedance when the associated electrodes are not selected has been deficient because of the restriction imposed on the driving pulse voltage for normal operation of the circuit due to spurious voltage pulses produced by the electrostatic coupling.